First time to see something like this, but till some one else come up with solution I can suggest the following:
* Check the installation requirements (specially folder permissions), may be something changed.
* Request a new password through forgetting password..
Following is summary of installation requirements as I get it (Yours should be OK also), revo 2.0.7 pl:
Checking PHP version: OK! Running: 5.3.5
Checking PHP for zlib dependency: OK!
Checking for SimpleXML: OK!
Checking if memory limit is set to at least 24M: OK! Set to 32M
Checking if sessions are properly configured: OK!
Checking if path_to_your_public_folder/core/cache directory exists: OK!
Checking if path_to_your_public_folder/core/cache directory is writable: OK!
Checking if path_to_your_public_folder/core/export directory exists: OK!
Checking if path_to_your_public_folder/core/export directory is writable: OK!
Checking if path_to_your_public_folder/core/packages directory exists: OK!
Checking if path_to_your_public_folder/core/packages directory is writable: OK!
Checking if path_to_your_public_folder/core/config/config.inc.php exists and is writable: OK!
Creating connection to the database: OK!
Checking to make sure safe_mode is off: OK!
Don’t forget to include your environment information always..
☆ A M B ☆